A battery is a device that produces electrical energy through electrochemical oxidation and reduction reactions, and has a wide range of various applications. For example, an application field of a battery is gradually expanding to a power source of handheld portable devices such as a mobile phone, a laptop computer, a digital camera, a video camera, a tablet computer, and an electric tool; various types of electric drive devices such as an electric bike, an electric motorcycle, an electric vehicle, a hybrid vehicle, an electric boat, and an electric aircraft; an energy storage system used to store electricity generated through new renewable energy or excess electricity of a power plant; and an uninterruptible power supplier for stable power supply to various types of information and communication devices including a server computer and a base station for communication.
A battery includes three basic elements; one is an anode including a material which oxides while emitting electrons during discharge, another is a cathode including a material which reduces while accepting electrons during discharge, and the other is an electrolyte which allows ions to move between the anode and the cathode.
A battery may be classified into a primary battery that cannot be reused after discharged, and a secondary battery that can be charged and discharged repeatedly due to at least partially reversible electrochemical reactions.
As a secondary battery, a lead-acid battery, a nickel-cadmium battery, a nickel-zinc battery, a nickel-iron battery, a silver-oxide battery, a nickel metal hydride battery, a zinc-manganese dioxide battery, a zinc-bromine battery, a metal-air battery, and a lithium secondary battery are known. Among them, a lithium secondary battery has a higher energy density, a higher battery voltage, and a longer lifespan than the other secondary batteries, and for these reasons, is attracting the greatest attention in commercial aspects.
A lithium secondary battery is characterized by intercalation and de-intercalation reactions of a lithium ion occurring at a cathode and an anode. That is, during discharge, a lithium ion de-intercalated from an anode material included in an anode moves to a cathode through an electrolyte and are intercalated into a cathode material included in the cathode, and vice versa when charging.
In the lithium secondary battery, because a material used as a cathode material significantly affects performance of the secondary battery, various attempts have been made to provide a cathode material having a high energy capacity while maintaining stability at high temperature as well as having low manufacturing costs. However, there is still a limitation in satisfying all the industrial performance standards with only one cathode material.
Recently, with the growing concerns on exhaustion of fossil fuels and air pollution, there is a drastic increase in demand for eco-friendly energy. In this context, commercialization of an electric drive vehicle such as an electric vehicle or a hybrid vehicle that is powered and runs by electrical energy supplied from a secondary battery is being accelerated by developed countries.
A speed of an electric drive vehicle is proportional to a power of a secondary battery. Accordingly, a control unit of the electric drive vehicle has a function of monitoring how much power the secondary battery can provide. Also, the control unit controls various types of driving devices including a motor to safely drive the electric drive vehicle within a range of maximum power the secondary battery can provide. Therefore, to optimize the travel performance of the electric drive vehicle, there is a need for a method for accurately calculating a power of the secondary battery.